The current standard of care for repairing severed tendons in the hand is to re-attach the two separated ends of the tendon with nothing but sutures. The two ends of the tendon are held together by the suture while the tendon heals. Surgical repair of tendons and ligaments, particularly flexor tendons, has been accurately described as a technique-intensive surgical undertaking.
The repair must be of sufficient strength to prevent gapping at the apposed end faces of the repaired member to allow the member to reattach and heal as well as to permit post-repair application of rehabilitating manipulation of the repaired member. Considerable effort has been directed toward the development of various suturing techniques for this purpose. Two strand, four strand, and six strand suturing techniques, primarily using locking stitches, have been widely used. There are a wide variety of suturing patterns which have been developed in an effort to attempt to increase the tensile strength across the surgical repair during the healing process. A common suturing technique in recent times is known as the Kessler repair, which involves the use of sutures that span, in a particular configuration or pattern, across the opposed severed ends of the tendon (or ligament). Evans and Thompson, “The Application of Force to the Healing Tendon” The Journal of Hand Therapy, October-December, 1993, pages 266-282, surveys the various suturing techniques that have been employed in surgical tendon repair. Further, two articles by Strickland in the Journal of American Academy of Orthopaedic Surgeons entitled “Flexor Tendon Injuries: I. Foundations of Treatment” and “Flexor Tendon Injuries: II. Operative Technique”, Volume 3, No. 1, January/February, 1995, pages 44-62, describe and illustrate various suturing techniques.
Generally, the tensile strength of a tendon repair increases with increased complexity of the suturing scheme. As set forth in the Evans and Thompson article, the loads at which failure occur across a sutured joint can vary between about 1,000 grams force to as much as about 8,000 grams force (or about 10 to 80 Newtons). There are at least two modes of potential failure, including breakage of the sutures or the sutures tearing out of the tendon. The Kessler and modified Kessler repair techniques tend to exhibit failure toward the low end of the range, for example, between about 1,500 to 4,000 grams force (or about 15 to 40 Newtons), which is much weaker than the original tendon and requires the patient to exercise extreme care during the healing process so as not to disrupt the tendon repair.
For instance, normal flexing of the fingers of the hand without any load generates forces of about 40 Newtons (N) on the tendon. Flexing with force to grasp something with the hand typically will place a force of about 60N-100N on the tendon. Finally, strong grasping of an object, such as might be involved in an athletic activity or in lifting of a heavy object can place forces on the tendons of the hand on the order of 140N or more.
The various suturing techniques also are rather complex and, therefore, difficult to reproduce and perfect as a technique, let alone perform it on the small tendons in the hand. Further, because they employ locking stitches, the two tendon ends must be brought to and maintained in the correct position relative to each other (i.e., with the ends in contact) throughout the entire procedure because the locking stitches do not permit future adjustment of the repair (as did some of the earlier techniques that do not use locking stitches).
Another significant difficulty with repairing lacerated and avulsed tendons in the hand, and, particularly, in the fingers is the need to re-route the severed tendon (usually the proximal tendon stump) through the pulley system of the finger joint. Specifically, when a tendon is severed or avulsed, the proximal tendon stump tends to recoil away from the laceration site toward the wrist. Accordingly, it often is necessary to make a longitudinal incision proximal to the laceration site in order to retrieve the proximal portion of the severed tendon and guide it through the pulley system of the finger back to the laceration site for reattachment to the distal tendon stump.
As reported in Evans and Thompson, at least one researcher has employed a Mersilene mesh sleeve having a diameter slightly larger than the tendon that is subsequently sutured to the two apposed tendon ends. Experimental failure loading as high as 10,000 grams force (100N) was reported using the sleeve. However, Mersilene, which is a non-degradable polyester, a common material used for manufacturing sutures used in orthopedics, has the disadvantage that human tissue will experience a local tissue response leading to adhesion of the polyester to tissue surrounding the repair site. This is undesirable in tendons and ligaments since the tendon must be able to glide freely relative to the surrounding tissue, such as the pulleys in the fingers. While a sleeve may be well suited for use with tendons and ligaments which are substantially cylindrical, it is less easily employed with tendons having a flat or ovaloid cross section. Moreover, any added bulk, in this case to the outside of the tendon, could be problematic as this repair would have to traverse the pulley system of the fingers.
U.S. Pat. No. 6,102,947 discloses another method and apparatus for repairing tendons that involves an implant that can be sutured to the tendon and which provides a splint running between the two tendon ends. The implant essentially comprises a wire bearing a first pair of wedges on one side of the midpoint of the wire with their pointed ends facing away from the midpoint and a second pair of wedges on the other side of the midpoint of the wire with their pointed ends also facing away from the midpoint (i.e., facing oppositely to the first pair of wedges). The first pair of wedges is pushed (or pulled) into one of the severed ends of the tendon and the other pair is pushed (or pulled) into the other severed end of the tendon. The wedges are sutured to the tendon and are retained within the tendon. This system provides high tensile strength to the repair.
Further, Ortheon Medical of Winter Park, Fla., USA developed and commercialized an implant for flexor tendon repair called the Teno Fix. The Teno Fix implant is substantially described in Su, B. et al, “A Device for Zone-II Flexor Tendon Repair: Surgical Technique”, The Journal of Bone and Joint Surgery, March 2006, Volume 88-A-Supplement 1, Part 1. The assembled implant comprises two intratendonous, stainless-steel anchors (in the form of a coil wrapped around a core) joined by a single multi-filament stainless steel cable. The implant is delivered to the surgeon unassembled, comprising a stainless steel cable with a stop-bead affixed to one end of the cable, two separate anchors with through bores for passing the cable therethrough, and another stop-bead with a through bore for passing the cable therethrough.
In practice, one of the anchors is advanced into a longitudinal intratendonous split (tenotomy) made in the proximal tendon stump so that the anchor sits within the longitudinal tenotomy and engages the tendon substance by capturing tendonous fibers between the core and the anchor. The other anchor is placed in the distal tendon stump in the same manner. Next, a straight needle with the stainless-steel cable attached thereto is threaded into the through-bore of the distal anchor from the small end of the anchor and is pulled through the center of the cut surface of the distal tendon stump until the stop-bead at the end of the cable opposite the needle contacts the distal anchor. The stainless-steel cable with the needle attached is then guided into the cut end of the proximal stump and through the through-bore of the anchor in the proximal stump from the large end of the anchor to the small end. The proximal stump of the tendon is then brought into contact with the distal stump by tensioning the cable, and the second stop-bead is placed over the stainless-steel cable at the proximal end of the proximal anchor. The second stop-bead is then crimped to lock it to the cable and the excess cable is cut so that the cable end is flush with the second stop-bead.
A disadvantage of the Teno Fix is the size of the tendon anchor, which is large and, thus, may add resistance to the tendon as it passes through the pulley system. Another disadvantage of the Teno Fix is the invasive nature of implanting the device wherein the entire track of skin over the tendon path must be incised in order to effect the implantation of the device. A third disadvantage is that the attachment of the anchor to the tendon is rather weak, reporting only about 46 Newtons of pull strength. These disadvantages are overcome by the subject and method described in this invention.
A disadvantage of most, if not all, of the prior art techniques discussed above is a high infection rate.